Various data/services are transmitted and provided in a network (E-UTRAN: evolved universal terrestrial radio access network) according to the asynchronous mobile communication system standard (3GPP). For instance, there are system information via BCH (broadcast channel), control message via PDCCH (physical downlink control channel), user traffic or control message via downlink/uplink SCH (shared channel), traffic or control message of broadcast/multicast service (MBMS) via downlink SCH or downlink MCH (multicast channel), initial uplink control message via RACH (random access channel) and the like.
The MBMS (multimedia broadcast multicast service) is a sort of a broadcast/multicast service and is the service that simultaneously transmits data packets to a plurality of user equipments. In this disclosure, ‘broadcast/multicast service’ can be replaced by one of different terminologies including ‘MBMS’, ‘point-to-multipoint service’, ‘MBS (multicast and broadcast service’ and the like. In the MBMS based on IP multicast, user equipments share resources required for data packet transmission and receive the same multimedia data. Hence, in case that a user equipment at a predetermined level, which uses MBMS, exists in the same cell, it is able to raise resource efficiency. As the MBMS has nothing to do with an RRC connection, a user equipment in an idle mode can be provided with the service.
Operational schemes of the MBMS can be categorized into two modes including a broadcast mode and a multicast mode. The broadcast mode is the mode that a single transmitter transmits data to all receivers on a sub-network. And, the multicast mode is the mode that at least one or more transmitters transmit data to at least one or more specific receivers. In the multicast mode, an intention to receive data needs to be delivered to a network and subscription and leaving is available.
In order to effectively operate the broadcast/multicast service, it is necessary to check the number of user equipments that attempt to receive a specific service. This kind of information is usable in determining an optimal scheme for providing the broadcast/multicast service. For instance, if the small number of user equipments are interested in the corresponding service, it may be more efficient to use a separate dedicated channel to provide the service to each of the user equipments. On the contrary, if a plurality of user equipments are interested in the corresponding service, it may be more efficient to use a common channel.
A method of counting user equipments attempting to receive a specific broadcast/multicast service (hereinafter named ‘MBMS counting’) is initiated in a manner that a network transmits an access information message to a user equipment via MCCH. If the user equipment attempting to receive the service is in an RRC connected state, counting can proceed using a dedicated channel or a RACH. On the other hand, if a user equipment is in an idle mode, an RRC connection request message is transmitted in accordance with a random access procedure using a RACH.
In the following description, the RACH and a random access procedure in WCDMA system are explained. First of all, a RACH is used to transmit data of a short length in uplink. And, such an RRC message as an RRC connection request message, a cell update message, a URA update message and the like is transmitted via the RACH. A logical channel such as CCCH (common control channel), DCCH (dedicated control channel) and DTCH (dedicated traffic channel) can be mapped to the RACH which is a transport channel. And, the RACH is mapped to a physical channel PRACH (physical random access channel).
Once a MAC (medium access control) layer of a user equipment indicates a PRACH transmission to a physical layer of the UE, the physical layer of the UE selects a single access slot and a single signature and then transmits a PRACH preamble in uplink. The preamble is transmitted for an access slot interval having a length of 1.33 ms. One of 16 kinds of signatures is selected and transmitted for a first predetermined length of the access slot. If the user equipment transmits the preamble, a base station transmits a response signal via a downlink physical channel which is a AICH (acquisition indicator channel). The AICH transmitted as a response for the preamble carries the signature selected by the preamble for a first predetermined length of an access slot corresponding to the access slot for transmitting the preamble. In this case, the base station transmits an positive response (ACK: acknowledgement) or a negative response (NACK: non-acknowledgement) to the user equipment using the signature carried by the AICH. If the user equipment receives ACK, it transmits an RRC connection request message to the network using an allocated radio resource. Thereafter, the network transmits a contention resolution message and an RRC connection setup message to the user equipment. If the user equipment receives NACK, it indicates a PRACH transmission to the physical layer of the UE again after an appropriate duration. Meanwhile, if the AICH corresponding to the preamble transmitted by the user equipment is not received, the user equipment transmits a new preamble by a power 1-step higher than that of the previous preamble after a predetermined access slot.